The present invention relates to devices for removing studs from a larger structure within which they are embedded, and, more particularly, to stud extractors for removing threaded and non-threaded studs which are flush with or recessed from the surface of the larger structure.
It is often necessary to remove studs from a matrix or larger structure within which they are embedded. Frequently, the stud is a threaded bolt whose head has been sheared off so that the shank of the bolt is flush with the surface of the larger structure, thereby making it impossible for the shank to be grasped by a tool such as a pair of pliers, a wrench, or the like. A common method of removing such embedded studs is to form a bore through the center of the stud, then insert a drill bit having reverse threads which bite into the wall of the bore and cause the stud to rotate with it, thereby backing the stud out of its threaded hole.
While this method is direct and uncomplicated, its application is somewhat limited. For example, should the stud be a smooth cylinder press fit into a bore, it may not be possible to remove the stud by the use of a threaded engagement between the stud and the stud extractor; the stud may simply turn within its bore. Furthermore, a stud may itself have reverse threads, requiring a bore to be drilled with a bit having reverse threads, then inserting a bit having right-hand threads to remove the stud.
A stud-removing device is shown in Royer et al. U.S. Pat. No. 2,600,924. That device includes a drill bit having projections for engaging the top surface of a stud which is flush with a supporting structure, and axially projecting lugs which are inserted into the bore formed in the stud to help center the bit as it is rotated. The projections dig into the stud as the drill bit is turned, causing the stud to rotate in a reverse direction and back out of its hole. A disadvantage of this device is that it requires a large surface area surrounding the bore formed in the stud to provide a surface to be engaged by the drill bit projections.
Accordingly, there is a need for a stud extractor which has applications in both right- and left-hand threaded studs, smooth studs, and studs which have broken off below the surface of the supporting structure or are located within recessed bores. Furthermore, there is a need for a stud extractor which requires a minimum of stud surface area to operate.